U.S. patent number 6,267,695 [Application Number 09/335,902] was granted by the patent office on 2001-07-31 for golf ball.
This patent grant is currently assigned to Bridgestone Sports Co., Ltd.. Invention is credited to Yutaka Masutani.
United States Patent |
6,267,695 |
Masutani |
July 31, 2001 |
Golf ball
Abstract
The invention provides a golf ball comprising a core and a
cover, wherein the cover consists of an outer layer and an inner
layer having a lower hardness than the outer layer. The cover inner
layer is formed with a plurality of recesses in its outer surface
and the cover outer layer is formed over the cover inner layer in
such a manner that the cover outer layer penetrates into the
recesses in the cover inner layer to form protrusions. The sum of
the cross-sectional areas of the protrusions at their base accounts
for 2-45% of the surface area of an imaginary smooth cover inner
layer. The protrusions have a height corresponding to 30-100% of
the thickness of the cover inner layer where no recesses are
formed. The ball receives a reduced spin and travel a distance upon
driver shots, but receives an increased spin and is easy to control
upon iron or sand wedge shots.
Inventors: |
Masutani; Yutaka (Chichibu,
JP) |
Assignee: |
Bridgestone Sports Co., Ltd.
(Tokyo, JP)
|
Family
ID: |
16221112 |
Appl.
No.: |
09/335,902 |
Filed: |
June 18, 1999 |
Foreign Application Priority Data
|
|
|
|
|
Jun 18, 1998 [JP] |
|
|
10-188294 |
|
Current U.S.
Class: |
473/377; 473/367;
473/368; 473/371; 473/374; 473/378; 473/600; 473/601; 473/602 |
Current CPC
Class: |
A63B
37/0003 (20130101); A63B 37/0097 (20130101); B29C
37/0082 (20130101); A63B 37/0004 (20130101); A63B
37/0031 (20130101); A63B 37/0033 (20130101); A63B
37/0064 (20130101); A63B 37/0065 (20130101) |
Current International
Class: |
A63B
37/00 (20060101); B29C 37/00 (20060101); A63B
037/04 (); A63B 037/06 () |
Field of
Search: |
;473/367,368,371,374,377,378,600,601,602 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shoap; Allan N.
Assistant Examiner: Kim; Paul D
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak &
Seas, PLLC
Claims
What is claimed is:
1. A golf ball comprising; a core and a cover enclosing the core,
wherein said cover consists essentially of an outer layer and an
inner layer having a lower hardness than the outer layer, the cover
inner layer made of a resinous material and is formed with a
plurality of recesses in its outer surface and the cover outer
layer is formed over the cover inner layer in such a manner that
the cover outer layer penetrates into the recesses in the cover
inner layer to form protrusions, the sum of the cross-sectional
areas of the protrusions at their base accounts for 2 to 45% of the
surface area of the cover inner layer where the cover inner layer
is spherical and not formed with the recesses, and the protrusions
have a height in a normal direction of at least 30% of the
thickness of the cover inner layer where no recesses are
formed.
2. The golf ball of claim 1 wherein the cross-sections of the
protrusions at their base have an average diameter of 0.5 to 4.0
mm.
3. The golf ball of claim 1 wherein the thickness of the cover
inner layer where no recesses are formed is 0.8 to 3.5 mm.
4. The golf ball of claim 1 wherein the cover outer layer has a
Shore D hardness of 40 to 70 and the cover inner layer has a Shore
D hardness of 10 to 55, the hardness difference therebetween being
at least 5 Shore D units.
5. The golf ball of claim 1, wherein said core is a solid core
having a diameter in the range of 28 to 38 mm.
6. The golf ball of claim 1, wherein said core has a deflection in
the range of 1.8 to 5.0 mm under a load of 100 kg.
7. The golf ball of claim 1, wherein said cover outer layer has a
thickness in the range of 1.0 to 3.0 mm and a Shore D hardness in
the range of 50 to 65.
8. The golf ball of claim 1, wherein the number of protrusions is
in the range of 60 to 600.
9. The golf ball of claim 1, wherein each protrusion has a height
of 0.8 to 3.5 mm.
10. The golf ball of claim 1 wherein the protrusions of the cover
outer layer fitted in the recesses in the cover inner layer satisfy
the following relationship: ##EQU5##
wherein A is the sum (mm.sup.2) of the cross-sectional areas of the
protrusions at their base, N is the number of protrusions, and T is
the thickness (mm) of the cover outer layer where no protrusions
are formed.
11. The golf ball of claim 1 wherein the cover inner layer is
selected from the group consisting of polyester elastomers, ionomer
resins, styrene elastomers, urethane resins and mixtures
thereof.
12. The golf ball of claim 1 wherein the cover outer layer is
selected from the group consisting of ionomer resins, polyurethane
resins, and polyester resins.
13. A golf ball comprising; a core, a cover inner layer and a cover
outer layer, wherein said cover outer layer has a higher hardness
than the cover inner layer, the cover inner layer is formed with a
plurality of recesses in its outer surface and the cover outer
layer is formed over the cover inner layer in such a manner that
the cover outer layer penetrates into the recesses in the cover
inner layer to form protrusions, the protrusions of the cover outer
layer fitted in the recesses in the cover inner layer made of a
resinous material and satisfy the following relationship:
##EQU6##
wherein A is the sum (mm.sup.2) of the cross-sectional areas of the
protrusions at their base, N is the number of protrusions, and T is
the thickness (mm) of the cover outer layer where no protrusions
are formed.
14. The golf ball of claim 13 wherein the cross-sections of the
protrusions at their base have an average diameter of 0.5 to 4.0
mm.
15. The golf ball of claim 13 wherein the cover inner layer has a
thickness of 0.8 to 3.5 mm where no recesses are formed.
16. The golf ball of claim 13 wherein the thickness of the cover
outer layer where no protrusions are formed is 0.5 to 4.0 mm.
17. The golf ball of claim 13 wherein the cover outer layer has a
Shore D hardness of 40 to 70 and the cover inner layer has a Shore
D hardness of 10 to 55, the hardness difference therebetween being
at least 5 Shore D units.
18. The golf ball of claim 13, wherein said core is a solid core
having a diameter in the range of 28 to 38 mm.
19. The golf ball of claim 13, wherein said core has a deflection
in the range of 1.8 to 5.0 mm under a load of 100 kg.
20. The golfball of claim 13, wherein said cover outer layer has a
thickness in the range of 1.0 to 3.0 mm and a Shore D hardness in
the range of 50 to 65.
21. The golfball of claim 13, wherein the number of protrusions is
in the range of 60 to 600.
22. The golfball of claim 13, wherein each protrusion has a height
of 0.8 to 3.5 mm.
23. The golf ball of claim 13 wherein the cover inner layer is
selected from the group consisting of polyester elastomers, ionomer
resins, styrene elastomers, urethane resins and mixtures
thereof.
24. The golf ball of claim 13 wherein the cover outer layer is
selected from the group consisting of ionomer resins, polyurethane
resins, and polyester resins.
Description
This invention relates to a golf ball comprising a core, a cover
inner layer, and a cover outer layer, and more particularly, to
such a golf ball in which the cover outer layer penetrates into the
cover inner layer to form protrusions therein.
BACKGROUND OF THE INVENTION
A variety of studies and proposals have been made to find a good
compromise between flight distance and "feel" of golf balls. For
solid golf balls comprising a solid core and a cover, one common
approach is to construct the core and the cover into multilayer
structures for adjusting their hardness and dimensions (including
diameter and gage).
For example, U.S. Pat. No. 5,439,227 discloses a three-piece golf
ball comprising a core, a cover inner layer and a cover outer
layer, the cover outer layer being harder than the cover inner
layer. U.S. Pat. No. 5,490,674 discloses a three-piece golf ball
comprising a solid core of inner and outer layers and a cover, the
core inner layer being harder than the core outer layer.
While the respective layers of most golf balls define smooth
spherical surfaces, the golf balls disclosed in U.S. Pat. Nos.
2,376,085 and 5,692,973 have a core which is provided with
outwardly extending protrusions for preventing the core from being
offset during injection molding of the cover therearound. The
protrusions in these golf balls are substitutes for the support
pins used during injection molding. These patents do not attempt to
positively utilize the shape effect of support pin-substituting
protrusions, but rather intend to avoid incorporation of a distinct
material in the cover, by forming the protrusions from the same
material as the cover.
Recently, JP-A 9-285565 proposes a two-piece solid golf ball in
which the solid core and cover, or adjoining layers of a multilayer
solid core or adjoining layers of a multilayer cover are provided
with irregularities. When hit, the ball gives a different feel to
the player, depending on the loft angle of the particular club with
which it is struck. This golf ball is improved in feel, but
insufficient in flight performance and spin. There is however, room
for further improvement.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball comprising a
core, a cover inner layer and a cover outer layer wherein the cover
inner layer is formed with recesses and the cover outer layer is
formed with protrusions fitted in the recesses, thereby achieving a
soft feel, a low spin rate when hit with a small loft angle club,
good flight performance, and good control when hit with an iron or
sand wedge.
It is well known from the study of strength of materials that a
beam or column supporting an axial compressive load gives rise to
the buckling phenomenon that as the load increases, uniform
compression becomes unstable and is shifted laterally whereby the
beam is bent. The invention has been made by applying the buckling
phenomenon to a golf ball. Specifically, when columns or
protrusions of different hardness are distributed in a
surface-adjoining region of a ball undergoing a large amount of
deformation, specifically the cover inner layer, the behavior of
vertical and horizontal components of the deformation that the ball
undergoes upon impact is made different from conventional balls.
Then the dependency on club of initial conditions (especially spin
rate) of the ball can be adjusted as desired.
The invention provides a golf ball comprising a core and a cover
enclosing the core, wherein the cover consists essentially of an
outer layer and an inner layer having a lower hardness than the
outer layer, the cover inner layer is formed with a plurality of
recesses in its outer surface and the cover outer layer is formed
over the cover inner layer in such a manner that the cover outer
layer penetrates into the recesses in the cover inner layer to form
convex protrusions. It has been found that the sum of the
cross-sectional areas of the protrusions at their base and the
height of the protrusions in a normal direction should be in
specific ranges; or the protrusions of the cover outer layer fitted
in the recesses in the cover inner layer should satisfy a specific
relationship to the thickness of the cover outer layer. The
construction where the protrusions on the cover outer layer are
fitted in the recesses in the cover inner layer in an optimum
manner has the following advantages. For driver shots, due to the
relationship between a high head speed and a small loft angle, the
impact force has a greater vertical component relative to the club
face so that the protrusions embedded within the cover inner layer
give rise to a buckling phenomenon (the ball is liable to
collapse), which provides a reduced spin rate and an increased
launch angle, resulting in a drastically increased carry. For short
iron shots, due to the loft angle, the impact force has a greater
horizontal component relative to the club face. Since the
protrusions within the cover inner layer do not give rise to a
buckling phenomenon except for the vertical component, satisfactory
spin performance is obtained.
In a first aspect, the invention provides a golf ball comprising a
core and a cover enclosing the core, wherein the cover consists
essentially of an outer layer and an inner layer having a lower
hardness than the outer layer, the cover inner layer is formed with
a plurality of recesses in its outer surface and the cover outer
layer is formed over the cover inner layer in such a manner that
the cover outer layer penetrates into the recesses in the cover
inner layer to form protrusions, the sum of the cross-sectional
areas of the protrusions at their base accounts for 2 to 45% of the
surface area of the cover inner layer provided that the cover inner
layer is not formed with the recesses, and the protrusions have a
height in a normal direction of at least 30% of the thickness of
the cover inner layer where no recesses are formed.
In a second aspect, the invention provides a golf ball comprising a
core, a cover inner layer and a cover outer layer, wherein the
cover outer layer has a higher hardness than the cover inner layer,
the cover inner layer is formed with a plurality of recesses in its
outer surface and the cover outer layer is formed over the cover
inner layer in such a manner that the cover outer layer penetrates
into the recesses in the cover inner layer to form protrusions, the
protrusions of the cover outer layer fitted in the recesses in the
cover inner layer satisfy the following relationship: ##EQU1##
wherein A is the sum (mm.sup.2) of the cross-sectional areas of the
protrusions at their base, N is the number of protrusions, and T is
the thickness (mm) of the cover outer layer where no protrusions
are formed.
When the ball is struck at a relatively high club head speed as
with a driver so that the ball is given a large impact force, that
force acts to cause the protrusions to buckle. On the other hand,
when the ball is struck at a relatively low head speed as with a
short iron so that the ball is given a small impact force, the
protrusions do not buckle. In the former case of large impact
force, the protrusions buckle so that the strength of the
protrusions of the cover outer layer embedded in the cover inner
layer does not substantially act and only the strength of the cover
inner layer formed softer than the protrusions contributes. This
results in a reduced spin rate and an increased carry. In the
latter case of small impact force, the protrusions do not buckle so
that the strength of the cover inner layer in a substantial sense
is a combination of the strength of the cover inner layer in itself
and the strength of the protrusions embedded therein, that is,
higher than the strength of the cover inner layer in itself by a
value attributable to the protrusions of higher hardness. Then the
cover inner layer exhibits a harder behavior, leading to an
increased spin rate.
The golf ball comprising the cover inner and outer layers with the
outer layer protrusions fitted in the inner layer recesses
according to the invention exerts the optimum flight performance
and controllability for a particular club used because the cover
inner layer having protrusions embedded therein exhibits a
different behavior depending on the magnitude of impact force and
the loft angle or number of a golf club.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view of a golf ball according
to one embodiment of the invention.
FIG. 2 is an enlarged view of the protrusion-recess engagement
between the cover outer and inner layers.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1, a golf ball according to the invention,
designated at 1, is illustrated as comprising a solid core 2, a
cover inner layer 3 enclosing the core 2, and a cover outer layer 4
enclosing the inner layer 3. All of these components are disposed
in a concentric fashion.
The solid core 2 is formed of a rubber composition primarily
comprising a base rubber containing polybutadiene rubber,
polyisoprene rubber, natrual rubber or silicne rubber as a main
component. For higher resilience, #polybutadiene rubber is
preferable. The polybutadiene used herein is preferably one
containing at least 40% of cis structure. In the base rubber,
another rubber component such as natural rubber, polyisoprene
rubber or styrene-butadiene rubber may be blended with the
polybutadiene if desired. Since a higher proportion of
polybutadiene rubber provides a higher resilience, the other rubber
component should preferably be less than about 10 parts by weight
per 100 parts by weight of polybutadiene.
In the rubber composition, a crosslinking agent may be blended with
the rubber component. Exemplary crosslinking agents are zinc and
magnesium salts of unsaturated fatty acids such as zinc
methacrylate and zinc acrylate, and esters such as trimethylpropane
methacrylate. Of these, zinc acrylate is preferred because it can
impart high resilience. The crosslinking agent is preferably used
in an amount of about 15 to 40 parts by weight per 100 parts by
weight of the base rubber. A vulcanizing agent such as dicumyl
peroxide is usually blended in the rubber composition, preferably
in an amount of about 0.1 to 5 parts by weight per 100 parts by
weight of the base rubber. In the rubber composition, zinc oxide or
barium sulfate is blended as an antioxidant or specific gravity
adjusting filler if desired. The amount of filler blended is
preferably about 5 to 130 parts by weight per 100 parts by weight
of the base rubber.
One preferred formulation of the solid core-forming rubber
composition is given below.
Parts by weight Cis-1,4-polybutadiene 100 Zinc oxide 5 to 40 Zinc
acrylate 15 to 40 Barium sulfate 0 to 40 Peroxide 0.1 to 5.0
Vulcanizing conditions include a temperature of 150.+-.10.degree.
C. and a time of about 5 to 20 minutes.
The rubber composition is obtained by kneading the above-mentioned
components in a conventional mixer such as a Banbury mixer, kneader
or roll mill. The resulting compound is molded in a core-shape mold
by injection or compression molding.
The solid core 2 is preferably made to a relatively large diameter
of 28 to 38 mm, more preferably 30 to 37 mm. A core with a diameter
of less than 28 mm would provide less resilience with a possible
reduction of flight distance. With a core diameter of more than 38
mm, the cover inner layer which must accommodate the protrusions of
the cover outer layer therein cannot be made sufficiently thick,
with a possibility that the protrusion-recess engagement become
less effective.
Preferably the core undergoes a deflection of 1.8 to 5.0 mm, more
preferably 2.5 to 4.5 mm under a load of 100 kg. The weight of the
core is usually about 12 to about 35 grams. The core is usually
formed to a single layer structure from one material although it
may also be formed to a multilayer structure of two or more layers
of different materials if desired.
The material of which the cover inner layer 3 is made is not
critical and may be either a resinous material or a rubbery
material insofar as it is relatively soft. Resinous materials
having good impact resistance are preferably used. Exemplary resins
include polyester elastomers, ionomer resins, styrene elastomers,
urethane resins, hydrogenated butadiene rubber and mixtures
thereof. Use may be made of commercially available ionomer resins
such as Himilan from Mitsui Dupont Polychemical K.K. and Surlyn
from E. I. Dupont, and polyester elastomers such as Hytrel from
Toray Dupont K.K.
The cover inner layer preferably has a Shore D hardness of 10 to
55, more preferably 15 to 40. If the cover inner layer has a Shore
D hardness of more than 55, the difference in hardness from the
cover outer layer becomes smaller with a possibility that the
embedment of cover outer layer protrusions in the cover inner layer
become less effective. With a cover inner layer hardness of less
than 10 in Shore D, the golf ball as a whole would become less
resilient.
According to the invention, the cover inner layer is formed around
the core by conventional injection or compression molding. It is
preferred that the cover inner layer is formed in its outer surface
with recesses at the same time as it is molded. Specifically, the
cavity of a mold for forming the cover inner layer is formed on its
inner surface with a plurality of protrusions corresponding to the
plurality of recesses. This mold enables that the cover inner layer
having a plurality of recesses in its outer surface be formed by
conventional injection molding. In some cases, after a smooth cover
inner layer is formed around the core, recesses can be formed in
the inner layer by engraving, drilling or any other means. Except
for the recesses thus formed, the remaining area of the cover inner
layer defines a substantially spherical surface. Within the
recesses, the convex protrusions of the cover outer layer are
formed as will be described below.
According to the invention, the cover outer layer material is
molded around the cover inner layer having a plurality of recesses
in its outer surface by conventional injection or compression
molding, whereby the cover outer layer having protrusions embedded
in the cover inner layer is formed.
Any of well-known cover stocks may be used in forming the cover
outer layer 4. The cover outer layer material may be selected from
ionomer resins, polyurethane resins, polyester resins and balata
rubber, with the ionomer resins being preferred. Use may be made of
commercially available 3.0 mm, between its base and its top. The
shape of the protrusions is not critical and they may be formed to
any suitable shape such as cylinder, cone, prism, pyramid,
frusto-cone or frusto-pyramid.
The protrusions of the cover outer layer fitted in the recesses in
the cover inner layer each have a cross-sectional area at their
base. The cross section of each protrusion at its base has a size
(which is an average diameter of cylindrical protrusions or an
average width of prism-shaped protrusions) of preferably 0.5 to 4.0
mm, more preferably 0.5 to 3.0 mm, and most preferably 1.0 to 3.0
mm.
The sum of the cross-sectional areas of all the protrusions at
their base should account for 2 to 45%, preferably 3 to 43%, more
preferably 3 to 40%, and most preferably 3 to 30% of the surface
area of the cover inner layer provided that the cover inner layer
is not formed with the recesses (differently stated, the surface
area of an imaginary sphere circumscribing the cover inner layer).
If the sum of protrusion areas is less than 2% of the surface area
of the smooth cover inner layer, the number or proportion of
protrusions embedded in the cover inner layer is too small for the
protrusions to exert their effect. If the sum of protrusion areas
is more than 45% of the surface area of the smooth cover inner
layer, the number or proportion of protrusions in the cover inner
layer is too large, failing to achieve the effect of the
invention.
As best shown in FIG. 2, the protrusion 4a has a height d in a
normal direction to the imaginary spherical surface (or in a radial
direction), and the cover inner layer has a thickness S where no
recesses are formed. The proportion of the height d of the
protrusion to the thickness S of the cover inner layer, that is,
(d/S).times.100, should be at least 30%. preferably 50 to 100%,
more preferably 60 to 100%, and most preferably 70 to 100%.
Protrusions with a height/thickness value of less than 30% ionomer
resins such as Surlyn from E. I. Dupont and Himilan from Mitsui
Dupont Polychemical K.K.
Additives such as titanium dioxide and barium sulfate may be added
to the cover stock for adjusting the specific gravity and other
properties thereof. Other optional additives include UV absorbers,
antioxidants, and dispersants such as metal soaps. The cover outer
layer may have a single layer structure of one material or be
formed to a multilayer structure from layers of different
materials.
The cover outer layer (excluding the protrusions embedded in the
recesses in the cover inner layer) preferably has a thickness of
0.5 to 4.0 mm, more preferably 1.0 to 3.0 mm, and a Shore D
hardness of 40 to 70, more preferably 50 to 65. The cover outer
layer should be harder than the cover inner layer. The difference
in hardness between the cover outer layer and the cover inner layer
should preferably be at least 5, more preferably 5 to 45, most
preferably 10 to 45 Shore D units. If the cover outer layer is
softer than the cover inner layer, effective deformation of the
protrusions would not occur.
In the golf ball of the invention, as shown in FIGS. 1 and 2, the
cover inner layer 3 is uniformly formed in its surface with a
plurality of recesses, and the cover outer layer 4 penetrates into
the recesses to form convex protrusions 4a therein.
The total number of protrusions embedded in the cover inner layer
(or the total number of recesses in the cover inner layer) is
generally 60 to 600, preferably 80 to 500, and more preferably 90
to 400. It is preferred that the protrusions be distributed on the
cover inner layer surface in a predetermined regular pattern. Any
well-known dimple arrangement such as regular octahedaral or
icosahedral arrangement is applicable to the distribution of the
recesses or protrusions. Each protrusion preferably has a height or
length of 0.8 to 3.5 mm, more preferably 1.0 to are unlikely to
buckle, so that the effect of protrusions embedded in the cover
inner layer is little exerted.
The thickness S of the cover inner layer where no recesses are
formed is preferably 0.8 to 3.5 mm, especially 1.2 to 3.0 mm.
Also as shown in FIG. 2, the cover outer layer has a thickness T
where no protrusions are formed, and the cross-sections of
protrusions at their base have an average diameter D (which is
simply a diameter if all the protrusions are identical). The
proportion of the average diameter D of the cross-sections of
protrusions at their base to the thickness T of the cover outer
layer, that is, (D/T).times.100, is preferably 20 to 500% (0.2 to 5
times), more preferably 30 to 300% (0.3 to 3 times). Outside this
range, the protrusions embedded in the cover inner layer would
become less effective, failing to achieve the objects of the
invention. If the cross-sectional shape of protrusions is not
circular, the diameter of a circle having substantially the same
area as the cross-sectional area is determined.
In the second aspect of the invention, the protrusions 4a of the
cover outer layer 4 fitted in the recesses in the cover inner layer
3 and the thickness T of the cover outer layer satisfy the
following relationship: ##EQU2##
preferably, ##EQU3##
wherein A is the sum (mm.sup.2) of the cross-sectional areas of the
protrusions at their base, N is the number of protrusions, which is
equal to the above-described total number of protrusions, and T is
the thickness (mm) of the cover outer layer where no protrusions
are formed. If the protrusions and the cover outer layer thickness
do not satisfy the above relationship, the effects of the invention
are not achieved.
There has been described a golf ball wherein the cover inner layer
is formed with a plurality of recesses and the cover outer layer
having a higher hardness than the cover inner layer penetrates into
the recesses so that convex protrusions of the harder cover outer
layer are embedded within the softer cover inner layer. When the
ball is struck with a driver or club having a smaller loft angle at
a relatively high head speed, the protrusions embedded in the cover
inner layer buckle so that the ball may undergo a substantial
deformation, leading to a drastic increase in flight distance by
virtue of the reduced back spin and increased launch angle. On the
other hand, when the ball is struck with a short iron or sand wedge
at a relatively low head speed, the protrusions embedded in the
cover inner layer do not buckle so that the ball is restrained from
deformation, which provides an increased back spin and maintains
ease of control.
As to performance, the golf ball of the invention, when hit with
iron and sand wedge clubs, exhibits excellent spin properties and
ease of control whereas when hit with a driver having a small loft
angle, the ball is increased in carry and total distance on account
of the reduced spin rate and increased launch angle.
The golf ball of this invention has a multiplicity of dimples in
its surface. The ball on its surface is subject to finishing
treatments such as painting and stamping, if necessary. The golf
ball as a whole preferably has a hardness corresponding to a
deflection of 2.6 to 4.5 mm, more preferably 2.8 to 3.8 mm, under a
load of 100 kg. The golf ball must have a diameter of not less than
42.67 mm and a weight of not greater than 45.93 grams in accordance
with the Rules of Golf.
EXAMPLE
Examples of the invention are given below by way of illustration
and not by way of limitation.
Examples 1-5 & Comparative Examples 1-6
Solid cores were formed by working a rubber composition of the
formulation shown below in a kneader and molding and vulcanizing it
in molds at a temperature of 155.degree. C. for about 15
minutes.
Core composition Parts by weight JSR BR01 50 JSR BR11 50 Zinc oxide
30 Dicumyl peroxide 1.2 Zinc acrylate 18 Note that JSR BR01 and
BR11 are polybutadiene rubbers by Japan Synthetic Rubber K.K.
Cover inner layers were formed around the cores by kneading resin
compositions of the formulation shown in Table 1 and injection
molding them in molds. The combination of core and cover inner
layer is shown in Table 2. Cover outer layers were formed around
the cover inner layers by injection molding cover stocks of the
formulation shown in Table 1. The combination of cover outer layer
with other components is shown in Table 2. Subsequent conventional
painting yielded three-piece golf balls of Examples 1-5 and
Comparative Examples 1-6.
The cover inner layer-forming molds used in Examples 1-5 and
Comparative Examples 1-4 had a plurality of projections distributed
on their cavity-defining inner surface in a regular octahedral
arrangement and corresponding to the protrusions reported in Table
2. At the same time as molding of the cover inner layer, it was
formed with a plurality of recesses in its surface. At the same
time as molding of the cover outer layer, it penetrates into the
recesses whereby the protrusions from the cover outer layer were
embedded in the cover inner layer. The shape and variants of the
protrusions are shown in Table 2.
These golf balls were examined for hardness, flight performance and
spin by the following tests. The results are shown in Table 2.
Ball hardness
Hardness is expressed by a deflection (mm) under a load of 100
kg.
Flight performance
Using a swing robot (Miyamae K.K.), the golf ball was struck with a
driver (Tour Stage X100 with a loft angle of 10.degree., by
Bridgestone Sports Co., Ltd.) at a head speed of 45 m/sec
(W#1/HS45). An initial velocity, carry, and total distance were
measured.
Spin
Using a swing robot (Miyamae K.K.), the golf ball was struck with
different clubs at different head speeds. A spin rate was
measured.
(1) driver (Tour Stage X100 with a loft angle of 10.degree., by
Bridgestone Sports Co., Ltd.) at heat speed 50 m/sec
(W#1/HS50)
(2) driver (the same as above) at head speed 45 m/sec
(W#1/HS45)
(3) No. 5 iron (Tour Stage X1000, by Bridgestone Sports; Co., Ltd.)
head speed 40 m/sec (I#5/HS40)
(4) sand wedge (Tour Stage X1000, by Bridgestone Sport:s Co., Ltd.)
head speed 25 m/sec (SW/HS25)
TABLE 1 Cover composition A B C D Hytrel 4047 100 Hytrel 3078 100
Surlyn 8120 65 Himilan 1855 35 Himilan 1605 50 Himilan 1706 50
Shore D hardness 40 30 51 65 Note that Hytrel is the trade name of
thermoplastic polyester elastomer by Toray Dupont K.K.; Surlyn is
the trade name of ionomer resin by E. I. Dupont; and Himilan is the
trade name of ionomer resin by Mitsui Dupont Polychemical K.K.
TABLE 2 Example 1 2 3 4 5 Core Diameter (mm) 34.8 34.8 34.8 34.8
34.5 Weight (g) 27.5 27.5 27.5 27.5 27 Hardness.sup.1) 2.9 2.9 2.9
2.9 2.9 (mm) Cover Composition B A C B A inner Thickness S 2.3 1.7
2.0 2.5 1.5 layer (mm) Shore D 30 40 51 30 40 hardness Cover
Composition C C D D D outer Thickness T 1.6 2.25 1.9 1.4 2.55 layer
(mm) Shore D 51 51 65 65 65 hardness Protrusions Number N 150 420
60 180 420 Height d (mm) 1.15 1.7 2.0 1.2 1.0 Shape cylinder cone
quadran- cone quadran- gular gular pyramid prism Cross-section 0.98
2.04 1.74 3.98 2.40 diameter.sup.2) (mm) Cross- 0.75 3.27 2.36
12.44 4.52 sectional area (mm.sup.2) Height/ 50 100 100 48 67
thickness.sup.3) (%) Area 2 30 3 45 43 proportion.sup.4) (%)
Parameter.sup.5) 0.610 0.908 0.913 2.843 0.941 Golf ball Weight (g)
45.18 45.28 45.3 45.1 45.31 Diameter (mm) 42.6 42.7 42.6 42.6 42.6
Hardness (mm) 3.15 3.02 2.79 2.5 3.0 Flight Initial 76.9 77.01 77.1
77.05 76.95 performance velocity W#1/HS45 (m/s) Carry (m) 214.9
215.6 216.7 217.1 216.3 Total (m) 223.5 221.4 228.2 230 229.6 Spin
rate W#1/HS50 2401 2385 2320 2200 2281 (rpm) W#1/HS45 2356 2290
2224 2125 2089 I#5/HS40 5418 5320 5120 5013 4932 SW/HS25 4890 4801
4697 4672 4492 Comparative Example 1 2 3 4 5 6 Core 34.8 34.5 34.8
34.5 36.7 36.7 27.5 27 27.5 27.5 29 29 2.9 2.9 2.9 2.9 2.9 2.9
Cover C A B A C A inner 1.7 2.7 1.9 1.5 2.1 1.7 layer 51 40 30 40
51 40 Cover D C D C D D outer 2.25 1.4 2.05 2.55 0.9 1.3 layer 65
51 65 51 65 65 Protrusions 50 60 420 150 -- -- 0.85 1.2 0.5 0.4 --
-- quadran- cone cylinder cylinder -- -- gular prism 1.41 7.14 0.40
4.15 -- -- 1.56 40.01 0.12 13.55 -- -- 50 44 26 27 -- -- 1.7 48 1.1
46 -- -- 0.626 5.098 0.193 1.629 -- -- Golf ball 45.03 45.28 45.2
45.32 45.3 45.28 42.7 42.7 42.7 42.6 42.7 42.7 2.8 3.03 3.2 3.05
2.85 2.5 Flight 77.03 77.12 76.92 76.95 77.13 76.95 performance
W#1/HS45 213.3 214 213.1 213.8 213.5 213.2 220.8 218 218.3 217.3
220 219.5 Spin rate 2623 2890 2650 2826 2590 2643 (rpm) 2480 2690
2451 2649 2435 2469 5135 5409 4960 5309 5043 4879 4680 4816 4275
4759 4423 4326 .sup.1) a deflection (mm) under a load of 100 kg
.sup.2) When the cross section of protrusions is not circular, the
cross-section diameter is the diameter of a circle of the same
area. .sup.3) (protrusion height d)/(cover inner layer thickness S)
.times. 100 .sup.4) (sum of cross-sectional areas of protrusions at
their base)/(surface area of imaginary smooth cover inner layer)
.times. 100 .sup.5) ##EQU4## A: the sum (mm.sup.2) of the
cross-sectional areas of the protrusions at their base N: the
number of protrusions T: the thickness (mm) of the cover outer
layer excluding the protrusions
It is evident from Table 2 that as compared with the comparative
golf balls, the golf balls within the scope of the invention
receive less spin when hit with a driver and equal or greater spin
when hit with No. 5 iron or sand wedge, on account of which the
inventive golf balls are drastically increased in carry and total
distance while their ease of control is equal or superior to that
of the comparative golf balls.
Although some preferred embodiments have been described, many
modifications and variations may be made thereto in light of the
above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *